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Basic Elements of a Koi Pond (See a note on Algae Control)

By Dr. Erik Johnson

To understand the basic requirements of a Koi pond, one need only bear in mind that the Koi grows to at least thirty inches as a mature fish. If the fish cannot grow this large in the pond they’re living in, this will cause stress and strain on the fish – both physically and mentally. Such strain will cause the fish to become vulnerable to environmental pathogens such as bacteria, and this susceptibility to infection will shorten the fishes’ lives.

Make sure the fish have enough room. Pond fish need ten gallons of water per inch of their length. So if you had a pond that was one thousand, five hundred gallons large, (1500 gallons) you would keep up to one hundred and fifty inches of fish. At first, this would be met with up to thirty fish of five-inch length. Later, as the fish grow, you would cut the number down through a process known as “culling” removing the least attractively marked fish, to cause the pond to house fifteen ten inch fish. Eventually, you’d cull the collection again and the fifteen-hundred gallon pond would house ten fifteen inch fish. In the pond’s fifth or sixth year, your thirty fish would have grown, and be “culled” to perfection, you will have removed twenty five “lesser” fish and retained FIVE large, thirty inch specimens of the finest coloration and pattern from your original group.

Koi and pond fish appreciate some light. The most successful ponds I’ve seen are situated in full sunlight, but there are plusses and minuses to this.
First, Koi and pond fish are healthier in sunny pond because the sunlight activates specific vitamins in their skin, adding in the absorption of calcium. Sunlight also enhances the coloration of the skin. Reds are deepened by sunlight.

The pond itself is healthier in full sunlight because the biological process of plants is fueled by sunlight. Plants do several wonderful things for pond water including the production of oxygen by day, the production of agglutinins that clarify water, and the support of microorganisms like Philodina, which actually clarifies water by eating bacteria. Plants also reduce nitrates (a chemical byproduct of filtration) which would otherwise accumulate in the pond.

If the pond is located in relative shade, plants that function in the shade should be chosen to try and capitalize on the above mentioned benefits. Your expectations as to how ferociously these processes occur should be realistically evaluated – your plants just won’t thrive as well without as much of the sun’s energy-fuel.
Keeping Koi indoors without natural sunlight is difficult to say the least. Keeping Koi and pond fish indoors mandates that the hobbyist would develop some means of natural or artificial nitrate reduction. Halide lighting which is suspended very near the water’s surface can grow some algae on the facilities’ bottom and duckweed can sometimes be grown on the surface of well lit reservoirs that communicate with the main facility (veggie filtration). Fish colors will fade if kept indoors without natural light.

Pond depth is irrelevant to Koi unless the pond is located in full sunlight or the pond is in Canada. If the pond is located in full sunlight and is very shallow, the pond can become inhospitably warm. Temperatures above ninety degrees are okay for Koi however these temperatures should be gradually accomplished, rather than shortly over one hot summer day. If the pond is deep enough, even in full sunlight, the pond’s temperature is relatively impervious to rapid swings in temperature.

If the pond is very shallow in a Canadian or similar wintertime zone, there can be risk that the ice will form deeply enough to impact the health of the fish. It is ideal to keep a hole in the ice open all winter long to allow the exchange of gases with the water. If the pond is 12 inches deep and the ice is 12 inches thick, no fish will survive. This is rarely a genuine problem but it does get pretty cold in some parts of the world.

Koi do not “require” any particular depth of the pond. You will find that if given the choice, they will spend their days in the shallows, basking in the sun like reptiles littering a rock. Their nights will be spent in the deeper sections of a pond. IF deprived of shallows OR deep spots, the Koi are not upset. They merely require fresh clean water and space to swim in.

For spawning, shallows are crucial. In nature, Koi spawn on plants in the shallows, scattering their hundreds of thousands of eggs all over the plants and gravel. If not provided with shallows or plant material, the fish will usually not spawn. This is not necessarily harmful to the fish.

Predation in ponds with shallows is no greater than in ponds that are deeper or which lack shallows. The reasons for this are many, but include that there are numerous Koi predators in the world. And many of these can dive in order to feed on fish. Since Koi usually cruise in the shallower levels of the pond looking for food, they are uniformly vulnerable to diving predators. To assert that a deeper pond simply avoids predation due to its depth is a myth. Koi will visit a Heron at the edge of any pond if they think it’s feeding time, and let’s not forget that the birds and otters of the world fish for a LIVING and aren’t in ANY way thwarted by something like pond depth.

Koi can grow to thirty inches in ponds as shallow as fourteen inches and they can grow to the same size in ponds nine feet deep. One of the very real problems with ponds over 3 feet deep is the exchange of oxygen with the surface. Without significant agitation and “turnover’ of the water of the pond, the deeper sections can be deficient in oxygenation. A pond which is eight or nine feet deep can be a real nuisance to aerate because without aggressive movement of the deeper layers of water to the surface, you will see the fish lingering near the top for the higher oxygen levels found there. This author converted a Gunnite swimming pool into a “koi” pond and at first, all the fish lingered at the top and in the shallow end. It was not until I dropped a turnover pump to the bottom of the deep end that the Koi decided it was safe to swim deep.

Two other problems with ponds over three-feet-deep include a very real defect in the ability to catch fish for examination, and also, the ability to clearly see the fish in the deepest parts of the pond without real Dragster filtration. Such technologically advanced filtration may be outside the comfort zone of the hobbyist who gets a pond in order to relax. It’s no fun to sit near a pond and think about something that you’re supposed to be maintaining or checking in a Dragster / High tech filtration system.

To succeed with pond fish, it’s as simple as honoring the components discussed in this document covering the relatively simple needs of Koi in terms of pond size, loading, depth and temperature.

If we wanted to go on, we could talk about a hundred different theories and opinions expressed in “absolutes” such as:
“A Pond must be XX inches deep”.
“A pond must have straight sides”.
“A pond must have an ultraviolet clarifier”
…And so on. These are all subjective mandates based on hobbyist preference and absolutely zero research. I don’t want to take away from the advantages and disadvantages of each assertion, but they are only assertions without science or research behind them. The answer to all of the above and more is that “The Koi do not care!”
If water quality and temperature can be stable and controlled in the pond you have, or the pond you’re building, you’ve got it licked.

Here's a list of the people who were on site and built my pond.

Ed Beaulieu, Jacob Carter & Tommy Hill (Bobcat), Mark Willoughby, Tony Watkins, "Cutie-John" Stehmeier, Joe "Nice Nips" Butler, Richard Panten, Mark Carter, Jeremy Anders, Lee Vought, Robby Mitchell, John Cenicola, Ryan Singleton, Joe Higginbotham, Dale "Whoa" Vnuk (Backhoe), Eric PondDigger Triplett, Jo Carter, Dan Bitcom (Videographer), Randy Young, Sam Brawner, BJ Linger, Chris "Shu" Tallerico, Mike Heron, David Panten, Andy "Super Scalp" Gundrum, Mike Reagor, Dave Blocksom, Brian Dahle, Ed and Tara Gallagher

Advanced Aquascape™ pond, two-belly design, 6x6 upflow aggregate filter w/ 9,000gph pump feeding falls.

More soon,

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